Shadow mask having all surfaces metal-coated

ABSTRACT

In a colour picture tube utilizing a colour selection electrode, a thin metal layer is applied onto at least one side of the colour selection electrode for the purpose of increasing the mechanical strength thereof.

United States Patent 1 1 Taniguchi et al.

1 SHADOW MASK HAVING ALL SURFACES METAL-COATED [75] Inventors: Masao Taniguchi; Hiromi Kauai,

both of Mobara'; Eiichi Yamazaki, lchihara, all of Japan [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: Apr. 11, 1973 [21] App]. No.: 350,067

[30] Foreign Application Priority Data Apr. 12, 1972 Japan 47-42437[U] [52] US. Cl 313/402; 29/25.14 [51] Int. Cl.H01j29/06;H01j29/08;H01j31/20 [58] Field of Search 313/85 S, 92 B, 402

[451 May 20, 1975 [56] References Cited UNITED STATES PATENTS 2,663,821 12/1953 Law 313/402 X 2,971,117 2/1961 Law 3,231,380 1/1966 Law 313/92 8 X Primary Examiner--Robert Sega! Attorney, Agent, or Firm-Dike. Bronstein, Roberts, Cushman & Pfund [57] ABSTRACT In a colour picture tube utilizing a colour selection electrode, a thin metal layer is applied onto at least one side of the colour selection electrode for the purpose of increasing the mechanical strength thereof.

10 Claims, 7 Drawing Figures Pmim numzoms SHEET 2 OF 2 F/G.2c

SHADOW MASK HAVING ALL SURFACES METAL-COATED BACKGROUND OF THE INVENTION This invention relates to a colour picture tube. more particularly to an improved construction of a colour selection electrode such as a shadow mask.

Widespread use of colour television receivers in recent years is remarkable, and various types of colour picture receiving systems have been developed and many improvements relating to colour picture tubes have been made. The colour picture tube is generally constructed such that electron beams emanated from an electron gun assembly are caused to impinge through a colour selection electrode upon predetermined positions of a fluorescent screen formed on the inner surface of a panel comprising a portion of the envelope. Among the colour selection electrodes are included a so-called shadow mask provided with a plurality of small circular perforations, a slit mask provided with a plurality of parallel stripe shaped slits or openings and a so-called slot mask wherein a plurality of transverse bridges are provided for each one of the stripe shaped openings. These colour selection electrodes are usually formed by providing perforations or slots through relatively thin soft iron sheets by photoetching technique. In order to improve the quality of the reproduced colour picture image of the colour picturing tube having such a colour selection electrode it is necessary to manufacture the openings to have an extremely high accuracy. For this reason. it is necessary for the soft iron sheet that the high precision openings can be readily formed therein, that is a soft iron sheet of low carbon content is preferred. However, such low carbon soft iron sheet is softer and has smaller toughness than iron sheets of higher carbon content. For this reason, the shadow mask of a black matrix type colour picture tube, for example a shadow mask type colour picture tube is provided with perforations having a diameter larger than that of the phosphor dots, thereby decreasing the mechanical strength of the colour selection electrode when compared with that utilized in the conventional colour picture tubes. Accordingly, the colour selection electrode is caused to vibrate by external shocks created while the colour picture tube is being handled or by the voice generated by the colour television receiver. This causes a missalignement of the openings of the colour selection electrode and corresponding phosphor dots thereby greatly degrading the colour purity of the reproduced colour pictures.

Further, when the colour selection electrode is locally heated by the impingement of the electron beams, the rigidity at such local areas is decreased so that a local stress is created by thermal expansion. This also degrades the colour purity of the reproduced colour picture.

Such decrease in the mechanical strength of the colour selection electrode also occurs in a post focusing type colour picture tube wherein the diameter of the perforations of the colour selection electrode is larger than a conventional colour picture tube, or a colour picture tube using a colour selection electrode having stripe shaped openings wherein the thickness of the colour selection electrode is made small for the purpose of decreasing the emission of the secondary electrons.

In order to prevent the decrease in the mechanical strength of the colour selection electrode, the thickness of the colour selection electrode is generally increased, the upper limit of the thickness is selected to be about 0.2 mm for the purpose of preserving the accuracy of the configuration of the perforations, and the use of thicker sheets is not advantageous.

SUMMARY OF THE INVENTION It is therefore an object of this invention to provide a colour picture tube having an improved colour selec tion electrode.

A further object of this invention is to provide a colour picture tube capable of preventing the missalignement of the phosphor dots on a fluorescent screen and the perforations of a colour selection electrode, for example a shadow mask.

Still further object of this invention is to provide a colour picture tube capable of improving the mechanical strength of the colour selection electrode.

Another object of this invention is to provide a colour picture tube having an improved colour selection electrode which is not deformed by external vibrations or local heat thereby preventing degradation of the colour purity.

Yet another object of this invention is to provide a colour picture tube having a colour selection electrode of a small secondary electron emission.

Still further object of this invention is to provide a colour picture tube provided with a colour selection electrode applied with a reinforcing metal layer on at least one surface thereof.

According to this invention, these and further objects can be accomplished by providing a colour picture tube of the class comprising a neck, a funnel, a panel, an electron gun assembly contained in the neck, a fluorescent screen formed on the inner surface of the panel and a colour selection electrode disposed close to the fluorescent screen for transmitting the electron beams emanated by the electron gun assembly to predetermined portions of the fluorescent screen, characterized in that a metal layer is applied onto at least one perforated surface of the colour selection electrode.

The metal layer can also be applied onto the entire surface of the colour selection electrode including the inner surfaces of the perforations through the colour selection electrode. The metal layer or layers are made of nickel or chromium and have a thickness of from 1 to 15 microns preferably from 1.5 to 5 microns.

BRIEF DESCRIPTION OF THE DRAWINGS The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. I is a diagrammatic longitudinal sectional view of a colour picture tube to which the invention is applicable;

FIGS. 2A through 2D are perspective views, partly in section, of typical colour selection electrodes and FIGS. 3 and 4 show sectional views of two examples of the colour selection electrodes embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I shows a basic construction ofa colour picture tube which comprises a neck I, a funnel 2, and a panel 3. An electron gun assembly 4 is contained in the neck 1 and a fluorescent screen 5 is formed on the inner surface of the panel 3. Further, a colour selection electrode 6 is disposed close to the fluorescent screen 5 for causing the electron beams emanated from the electron gun assembly 4 to impinge upon the predetermined portions of the fluorescent screen 4.

As the colour selection electrode 6 various forms may be used such as the one provided with a plurality of small circular perforations as shown in FlG. 2A, the one provided with a plurality of parallel stripe shaped slits 62 as shown in FIG. 2B, the one wherein a plurality of transverse bridges 63 are provided for each slit as shown in FIG. 2C or the one wherein the transverse bridges 63 are staggered in the vertical direction as shown in FIG. 2D. FIG. 3 is an enlarged perspective view of a portion of the colour selection electrode 6 shown in FIG. 2A and constructed in accordance with the invention, in which metal layers 65 for reinforcing the colour selection electrode are applied on both sides as well as on the inner surfaces of the perforations of the colour selection electrode.

Where the metal layers 65 are applied on the entire surface of the colour selection electrode 6 it is possible to increase the mechanical strength thereof even when the diameter of the perforations is increased for the purpose of improving the percentage of transmission of the electron beams or even when the thickness of the colour selection electrode is decreased so that a large stress will not be caused by external vibrations or local heating. As a result, it is possible to positively prevent the missalignement of the phosphor dots and corresponding perforations of the colour selection electrode thus assuring a high colour purity of the reproduced colour pictures.

The colour selection electrode of this construction can be prepared in the following manner.

A plurality of small circular perforations are formed through a low carbon iron sheet by means of conventional etching technique and after shaping the perforated sheet to have a predetermined configuration or after the perforated sheet has been subjected to a further light exposure and an etching process the metal layer of nickel or chromium is applied onto the colour selection electrode to a thickness of from 1 to microns by any well known technique such as electroplating or electroless plating, When the thickness of the metal layer 65 exceeds l5 microns the diameter of the perforations will be decreased by more than 30 microns whereby the purpose of enlarging the perforations will be lost. If the thickness of the metal layer is smaller than 1 micron. sufficient mechanical strength will not be obtained. A preferred range of the thickness of the metal film is from about 1.5 to 5 microns in the case of an electrolytically applied nickel plating. preferably from about 2 to 3 microns. In the case ofa nickel layer applied by non electric plating technique the strength of the plated layer can be improved by baking it at a temperature of about 250 to 480C. A range of from 250 to 300C is the most suitable for the heat treatmcnt to prevent deformation of the colour selection electrode caused by the heat treatment. The colour sc lcction electrode should be designed such that the provision of the reinforcing metal layer will not decrease the percentage of transmission of the electron beams emitted by the electron gun assembly To this end. the diameter of the perforations is made slightly larger than that of the prior art design so that the diameter of the perforations will have the desired value when the inner surfaces of the perforations are coated by the metal layer. We have confirmed that the mechanical strength of the colour selection electrode was improved greatly by applying metal layers over the entire surface of the colour selection electrode. When black metal layers such as blackened nickel platings are used. the heat generated by the local heating caused by the collision of the electron beams can be dissipated efficiently by radiation thus preventing deformation of the colour selection electrode. For this reason. the missalignement between the phosphor dots and corresponding perforations of the color selection electrode can be greatly decreased, thereby improving the colour purity of the reproduced colour picture. Further, when the surface of the metal layer is roughened it is possible to improve the heat dissipation of the colour selection electrode.

in the modification shown in FIG. 4 layers 67 of a substance such as graphite capable of suppressing the emission of secondary electrons are applied on the metal layers for the purpose of decreasing the secondary electron emission from the colour selection electrode.

Although in the foregoing embodiments. metal layers are applied on the entire surface of the colour selection electrode it is also possible to improve the mechanical strength thereof even when such metal layer is applied to only one side of the colour selection electrode. lt will be readily understood that the metal layers can also be applied to other types of the colour selection electrodes shown in FIGS. 28, 2C and 2D.

What is claimed is:

I. A colour picture tube of the class comprising a neck. a funnel, an electron gun assembly contained in the neck, a fluorescent screen of colour display type coated on the inner surface of the panel in triads and a colour selection electrode, made of iron and having a plurality of perforations, adjacent to the fluorescent screen for transmitting the electron beams emanated by the electron gun assembly to predetermined portions of the fluorescent screen, and a metal layer applied onto all surface areas of the colour selection elec trode for increasing the strength of said colour selection electrode.

2. The colour picture tube according to claim 1 wherein said metal layer is made of nickel.

3. The colour picture tube according to claim 1 wherein said metal layer is made of chromium.

4. The colour picture tube according to claim 1 wherein said metal layer has a thickness of l to 15 mi crons.

5. The colour picture tube according to claim 1 wherein said metal layer has a thickness of l.5 to 5 microns.

6. The colour picture tube according to claim I wherein said metal layer has a thickness of 2 to 3 mi- CTOHS.

7. The colour picture tube according to claim 1 wherein said metal layer is formed by electrolytic plat ing technique.

8. The colour picture tube according to claim 1 wherein said metal layer is formed by clectroless plating technique.

9. The colour picture tube according to claim 8 wherein said metal layer is heat treated at a temperature of from 250 to 480C.

10. The colour picture tube according to claim 8 wherein said metal film is heat treated at a temperature of from 250 to 300C. 

1. A colour picture tube of the class comprising a neck, a funnel, an electron gun assembly contained in the neck, a fluorescent screen of colour display type coated on the inner surface of the panel in triads and a colour selection electrode, made of iron and having a plurality of perforations, adjacent to the fluorescent screen for transmitting the electron beams emanated by the electron gun assembly to predetermined portions of the fluorescent screen, and a metal layer applied onto all surface areas of the colour selection electrode for increasing the strength of said colour selection electrode.
 2. The colour picture tube according to claim 1 wherein said metal layer is made of nickel.
 3. The colour picture tube according to claim 1 wherein said metal layer is made of chromium.
 4. The colour picture tube according to claim 1 wherein said metal layer has a thickness of 1 to 15 microns.
 5. The colour picture tube according to claim 1 wherein said metal layer has a thickness of 1.5 to 5 microns.
 6. The colour picture tube according to claim 1 wherein said metal layer has a thickness of 2 to 3 microns.
 7. The colour picture tube according to claim 1 wherein said metal layer is formed by electrolytic plating technique.
 8. The colour picture tube according to claim 1 wherein said metal layer is formed by electroless plating technique.
 9. The colour picture tube according to claim 8 wherein said metal layer is heat treated at a temperature of from 250* to 480*C.
 10. The colour picture tube according to claim 8 wherein said metal film is heat treated at a temperature of from 250* to 300*C. 